US Republican presidential candidate Ted Cruz appeared poised for victory over Donald Trump in Wisconsin last night.

Mr Cruz has been presenting himself as a possible unification candidate for Republican voters despite a Senate tenure marked by bitter feuds.

The first-term US senator from Texas is trying to make the case he is the last remaining Republican candidate not named Trump with a pathway to the party's presidential nomination and the best choice left for Republicans who cannot bring themselves to vote for the New York billionaire.

Wisconsin will be a test of whether his strategy will work. Opinion polls show he had opened up a convincing lead on front-runner Trump, with Ohio Governor John Kasich running third.

"The entire country is looking to Wisconsin," Cruz said. "What we are seeing in Wisconsin is the unity of the Republican Party manifested."

Mr Trump brought wife Melania on stage this week in Milwaukee, an apparent effort to repair his image with women who polls show overwhelmingly oppose him.

"No matter who you are, a man or a woman, he respects everyone equal," she told the crowd.

In the Democratic race, US Senator Bernie Sanders of Vermont had a slender lead in opinion polls in Wisconsin over front-runner Hillary Clinton and was trying to add to his momentum after winning five of the last six contests. He still faces a tough task in defeating the favoured Clinton for the nomination for the November 8 election.

Playing peacemaker is an unlikely role for Mr Cruz, who forced the US government to shut down for six days in 2013 in a budget fight with President Barack Obama. Republicans ended up being blamed for the shutdown and Cruz's relationship with Senate Republicans leaders has been stormy.

But enmity toward Mr Trump among many is such that Mr Cruz can now count five of his former rivals for the presidential nomination among his backers, including Senator Lindsey Graham of South Carolina, who said earlier this year that the choice between Trump and Cruz was like the choice between "being shot or poisoned".

Mr Cruz has taken steps to warm up his image. He told Fox News anchor Megyn Kelly in a town hall meeting this week in Madison, Wisconsin, that he wished he had done a "better job reaching out" to his Senate colleagues and building a broader coalition.

But he is as strident as ever when it comes to the presidential race. He told reporters that only he and Mr Trump had the ability to earn the 1,237 delegates necessary to win the nomination outright.

He said if no candidate received the required number of delegates, Republicans' choices at a contested nominating convention in July would be limited to him and Trump, because Kasich had not won the minimum eight states to get on the convention ballot.

Mr Cruz rejected talk that establishment Republicans might seek to nominate a new face at the convention, with names circulating like House of Representatives Speaker Paul Ryan or 2012 nominee Mitt Romney. He called it a "fevered pipe dream of Washington that at the convention they will parachute in some white knight".

"It ain't going to happen. If it did, the people would quite rightly revolt," said Cruz.